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Abstract

Most people would take no issue with Shakespeare's famous line in Hamlet describing humans as unique among the animals. But exactly how this singularity can be explained is not so clear. Many animals have larger brains than humans, certain birds demonstrate planning for the future, and the linguistic abilities of chimpanzees such as Nim Chimpsky continue to impress many observers. Research has often blurred the distinction between human and animal intelligence, but undaunted, into this fertile territory the distinguished cognitive neuroscientist Michael S. Gazzaniga ventures with impressive knowledge and enthusiasm.

Human: The Science Behind What Makes Us Unique is an ambitious book that embraces wide-ranging disciplines — neuroanatomy, neurology, psychology, genetics, and cognitive science, as well as anthropology, language, painting, philosophy, ethics, and artificial intelligence. The text is packed with lucid explanations of recent findings from investigations taking general aim at the question of what it means to be human.

Not a quick read for a few spare hours, many passages are detailed and challenging, sometimes requiring a second reading. And for more focused study, a long reference list is also provided. But this book is steadily entertaining, informal while never superficial, and often startlingly original.

In considering the evidence for prehistoric humans' belief in an afterlife that implies a distinction between body and soul, for example, Gazzaniga asserts that the Cro-Magnons were dualists. Although much here will be heavy going for the non-professional reader, the lively prose and inherent interest of the topic will sustain and reward those who persevere.

A COGNITIVE SCIENTIST'S PERSPECTIVE

For neurologists, much of the information in Human will be familiar, but the perspective of a cognitive neuroscientist with a firm grasp of many fields apart from clinical medicine will still be illuminating. The pages sparkle with new data and insights that may not come across the desk of a busy clinician or basic scientist. Utterly unpretentious, the author treats the reader to a wealth of material integrated into a satisfying whole with an expansive scope. One is intrigued by observations, for example, that humans can easily be taught to be afraid of snakes but not flowers, and that out-of-body experiences have been associated with stimulation of the right angular gyrus.

The book is divided into four sections. The first is a relatively brief account of the brains of humans and other animals, most notably the chimp, which naturally assumes a prominent place in this account as the closest of our primate relatives. The evidence clearly points to human brains being bigger than expected for an ape, with the neocortex, cerebellum, and white matter all contributing to this expansion. These structural advantages are far from trivial, endowing humans with a much greater capacity to understand the thoughts, beliefs, and desires of others. Imagining a date with a chimp, Gazzaniga finds many uncomfortable differences that extend to well more than just language, and wryly concludes: “Make my date a Homo sapiens. ”

The next section takes up the complex social world of human beings. “We are social to the core,” boldly claims the author. This characteristic, a result of evolutionary selection, is then deftly woven into a penetrating discussion of current neuroscientific study relevant to modern society on such topics as morality, empathy, and altruism. “As the neurobiology of moral behavior becomes fleshed out …” it is heartening to learn that the violent, amoral, purposeless depravities of humans may have a countervailing force in our brains. Among the many implications of this emerging area of neuroscience, the concept of theory of mind — the ability to understand and predict the behavior of other people — is taken up at several points, and the interesting recent data on mirror neurons come into play as helping us understand a host of normal and abnormal social behaviors.

In the third section, we are escorted through some of the cognitive domains of humankind, including the arts, philosophy, and the ever-intriguing phenomenon of consciousness. Once again, chimps do not fare well, exhibiting little, if any, creativity, while the astonishing paintings and music produced by humans exemplify creative endeavor firmly rooted in neural structures such as the prefrontal cortex. The appreciation of beauty also appears to be represented in the brain, this time the orbitofrontal cortex, implying a particularly distinctive feature of human neural architecture.

The philosophical position of dualism reflects the unique human capacity to form concepts about imperceptible things; even as that capability perpetuates mysterious entities such as soul or spirit, so too does it manifest itself as the curiosity that is a cornerstone of science. Consciousness is envisioned as an emergent property of the brain, a familiar idea, but Gazzaniga's twist is that the unitary conscious experience humans have can be attributed to the left hemisphere “interpreter” that makes sense of it all.

The final section considers a future in which technical advances may enhance or even supercede brain structure and function. Cochlear implants are presented as the most successful neural implant so far — a mechanical device that has essentially taken over a brain function. And such a device may be only the beginning. Researchers have begun implanting silicon chips into monkey and rat brains in an effort to restore lost cognitive function, and this approach is being contemplated for use in the hippocampus of people with Alzheimer disease to improve memory. Computers, robots, artificial intelligence, and even artificial chromosomes also receive substantial attention. A consistent theme, however, is that it is difficult if not impossible for any non-living thing to come even close to the uniqueness of human beings.

THE NOTION OF BRAIN CONNECTIVITY

Concluding with a short Afterword, Gazzaniga returns to the notion of brain connectivity to explain what is special about humans. Compared to chimps, “…I think the crucial difference is that we aren't hooked up the same.” True to his career interest in the corpus callosum, which allows “…more punch per cubic inch of brain,” he explains how connectivity enables hemispheric specialization, increased neural efficiency, and a host of cognitive abilities that our closest living relatives cannot claim. Like other animals, we are “…constrained by our biology …” but unlike them,…the ability to wish or imagine that we can be better is notable.” With characteristic wit, he ends his book with a robust, “Am I ever glad I am not a chimp!”

Science writing is vital for expressing in a readable way the extraordinary findings of scientists for popular as well as professional consumption. This book succeeds admirably as a new addition to this genre — scholarly, comprehensive, and fascinating for anyone interested in how the singular capacities of Homo sapiens can be understood. Shimmering with exceptional content, Gazzaniga's writing is, at the same time, delightfully self-effacing and engaging. After all, who better to write about chimps and humans than a neuroscientist who admits that he was a member of the fabled Animal House at Dartmouth College? •

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